This invention relates generally to the manufacture of magnetic structures and electrical reactive components in particular, multilayer coils employing printed circuits.
The ongoing integration and miniaturization of components in the electronic industry has greatly accelerated the densification of electronic circuitry. Transistors, resistors and capacitors have all but disappeared into integrated circuits, except where discrete devices are required. On the other hand, electrical inductors, i.e., coils and transformers, have not changed as significantly. Simple bulky wire wound coils and transformers abound in modern day electronic circuitry, mingling with far smaller integrated circuits of almost incredible complexity. Although coils see use as radio frequency chokes and filters, the most frequent applications are for motive power by magnetic attraction (motors and solenoids) and, of course, for transformers. Transformers serve in AC and pulse circuits as power supply components, isolation devices and electromagnetic
The present application focuses on coils as used for transformers in power supplies, for example, in DC to DC converters. However, there are many other applications. The heaviest bulkiest component of most power supplies is the transformer. Thus, miniaturization of the power supply depends on miniaturization of the transformer. The power supply of the future will be a surface mount device attached to a printed circuit board just like integrated circuit component. Present day bobbin wound transformers are incompatible with surface mount technology. Moreover, because of the lack of uniformity in the winding operation, parameters of nominal inductance, self-resonance, leakage inductance and self-capacitance, for example, are relatively difficult to control to tight tolerances.
In the past, there have been attempts to make multilayer coils which have not met with great success because of limitations in the manufacturing procedures. It is known, of course, to make a planar spiral type coil conductor pattern on a printed circuit board. The prior art also suggests stacking of a number of separately manufactured planar coil substrates and interconnecting the planar coil layers. The manufacturing obstacles and interconnection technology, however, leave much to be desired.